The disclosure is aimed in particular at an exhaust-gas recirculation system for a turbocharged internal combustion engine of a motor vehicle, an internal combustion engine and a method for exhaust-gas recirculation for a turbocharged internal combustion engine of a motor vehicle.
Exhaust-Gas Recirculation (EGR) serves to minimize nitrogen oxide emissions generated during the combustion. Here, the already burned exhaust-gas is supplied to the fresh-air flow supplied to the engine, and the mixture thereby generated is burned in the engine with a supply of fuel.
Ever more stringent legal requirements demand the reduction of NOx emissions and an improvement of the exhaust-gas recirculation control system. As more EGR is recirculated there is less enthalpy on a turbocharger turbine, and less oxygen in the exhaust-gas resulting in progressively richer air-fuel ratio in the combustion chamber.
Present controllers base EGR rate on the mass air flow (MAF), in which feedforward setpoint values for the exhaust-gas recirculation valve are generated taking into consideration the present operating point of the engine, usually speed and load and/or rated torque. Some model-based adaptations are partially included, in which the theoretical flow area of the exhaust-gas recirculation valve is controlled. This approach however has problems with regard to stability, because a pressure ratio across the valve may be measured or estimated, and because there are adverse effects caused by fluctuations as a result of pumping of the engine, sensitivities around a pressure ratio of one, and by impurities with fine dust or solid bodies.
Furthermore, sensors for the mass air flow are liable to durability problems, which can lead to a large offset in the measurement. Said durability problems occur in particular during long periods of city driving.
A different controller for exhaust-gas recirculation, which has been developed for EURO VI+ applications, uses an oxygen sensor arranged in the intake manifold, also referred to as an FMAN sensor, in order to regulate the oxygen concentration. In this way, it is sought to obtain optimum combustion in the cylinders of the engine. Said method is however expensive and involves a considerable amount of expenditure in the revision of existing oxygen sensors. For example, the stability of the heating circuit and the dynamic characteristics of the pump cells use a continuously varying factor for the pressure correction.
The inventors have recognized the aforementioned disadvantages and disclose herein a system and methods for accurate monitoring and delivery of desired air charge oxygen content. The object of the present disclosure is the accurate control of EGR rate to produce desired air-fuel ratio. This is achieved by monitoring a turbocharger speed and exhaust-gas lambda.
Through the use of the lambda value and the speed or rotational speed of the turbocharger, which are relatively simple to determine, it is possible to dispense with the difficult and unreliable determination of the mass air flow. It is thus possible to provide a stable method which furthermore reduces the fuel consumption of the engine.
The present disclosure provides systems and methods for adjusting an exhaust gas recirculation rate to provide accurate air-fuel ratio. The disclosure provides a method for calculating an exhaust-gas recirculation rate based on a measured exhaust-gas lambda and a turbocharger speed. Through the use of the exhaust-gas lambda and the turbocharger speed it is possible to calculate an exhaust-gas recirculation rate while dispensing with the difficult and unreliable determination of the mass air flow for determining an exhaust-gas recirculation rate, thus providing a stable method which further reduces fuel consumption and emissions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Further, the inventors herein have recognized the disadvantages noted herein, and do not admit them as known.